1. Field of the Invention
The present invention relates to an impact-absorbing steering column device, and more specifically, to a technology to reduce the manufacturing cost, facilitate setting of impact-absorbing characteristics of the device, etc.
2. Related Background Art
When a car collides with another car, a building, or the like, the driver in some cases comes into a secondary collision due to inertia and suffers serious damage to his head or chest. Recently, cars and automobiles largely employ, in order to avoid such trouble, an impact-absorbing steering shaft or an impact-absorbing steering column device. An impact-absorbing steering shaft is generally arranged such that the length of a steering shaft on the steering wheel side is reduced when the driver comes into a secondary collision. For this arrangement, the steering shaft is divided into an outer shaft and an inner shaft, and these shafts are engaged with each other to be mutually slidable by serration, etc. An impact-absorbing steering column device is arranged, for example, such that a steering column moves forward together with a steering shaft when the driver comes into a secondary collision. For this arrangement, plastic pins are generally used for connecting a bracket fixed to the car body (a dashboard or the like) (hereinafter called the body-side bracket) with the steering column so that the pins are broken due to the impact load at the time of the secondary collision and causes the steering column to move forward.
Normally, the impact-absorbing steering column device is provided with an impact absorbing means between the body-side bracket and the steering column so as to gradually absorb the impact energy which the steering column moves forward. For example, Japanese Utility Model Application Laid-Open No. 5-75057 discloses such arrangement in which an impact energy absorbing member is interposed between an upper bracket for supporting an upper part of a steering column and the steering column and the impact energy absorbing member is elongated to be plastically deformed when the steering column moves forward. This impact energy absorbing member is formed by punching a steel plate into the form of a pantograph or a waveform, and the fore end of the impact energy absorbing member is welded to the steering column whereas the rear end thereof is locked by a pin inserted through the car body-side bracket. Also, in Japanese Patent Application Laid-Open No. 7-215221, there is disclosed an impact energy absorbing member formed of a band-shaped steel plate, as well as another impact energy member punched from a steel plate and has a pleated elongated portion. The band-shaped steel plate has one end secured to the body-side bracket (or the steering column) and is drawn to be deformed by a drawing portion which is formed on the steering column side (or the body-side bracket) when the steering column is moved forward.
In the above-mentioned impact-absorbing steering column device, since the impact energy absorbing member is made of a steel plate, it requires a great cost to produce a press metal mold for punching the member. Also, since the weight per unit area of the steel plate is large, if an impact absorbing stroke is made large, the whole weight of the steering device also becomes large. Also, if the impact energy absorbing member is made in the form of a pantograph or wave form, a large amount of waste material is generated when the impact energy absorbing member is punched, so as to bring about a very poor yield of material. For the steering device in which an impact energy absorbing member is welded to a steering column or the like, the process of assembling the steering device includes a welding work, which inevitably causes a decline of the assembling workability and deterioration of working environments. In addition, in a steering device of this type, it is desirable to set the impact absorbing characteristics freely, which, however, requires a great cost when the specifications are altered, because a press metal mold is used for punching the impact absorbing member.